My experience with the two levels of gratitude has been similar to Steve's. I've found, though, that there is a third level that extends and enriches the other two.
This is the attitude of being grateful to
someone or something. If you have someone to thank, and that someone receives your thanks, the whole experience of gratitude is different. Before, the gratitude is inside you, an internal attitude. When you extend that gratitude to
someone, it becomes an interaction, a social act, a kind of bonding between you and the one you're thanking. The gratitude takes on a whole new dimension, and is that much more rewarding. At least, this has been my experience. :-)
I write about this a lot more here: Druid Journal » Blog Archive » Impact of Druidism on Everyday Life: Requited Gratitude